A large number of different types of anchors have been proposed for mooring vessels, and various improvements have been suggested for the types of anchors commonly in use. Designs and improvements have typically been directed to aims such as increasing the water depth in which anchoring can be carried out, increasing strength, increasing manoeuvrability and increasing efficiency, that is maximum weight of a vessel that can be anchored with an anchor of given weight.
A shovel or plough like part of an anchor that digs itself into the ground to secure the anchor in position is generally known as a fluke, and a body of an anchor to which a chain is usually secured from the vessel is generally known as a shank. In some anchors the fluke is pivotally connected to the shank so that the angle between the fluke and shank can increase as the fluke buries itself into the seabed. Other anchors have a fluke that is rigidly connected to a shank to improve strength or for use in particular types of ground. These are generally known as fixed fluke anchors.
One problem with conventional fixed fluke anchors that has not been adequately addressed to date is reliably setting an anchor so that the anchor is correctly orientated when deployed, remains in place and is retrievable when desired with the minimum of delay and without the anchor getting snagged or stuck in the ground. Retrieval may be particularly problematic when a vessel is moored in very deep water, when the anchor has been deployed for a considerable length of time, if the bottom is heavy, with sticky clay for example, if the anchor has sunk through many layers of silt and mud and then become embedded in a heavier deposit or where the anchor is especially large and heavy. These issues may arise in particular when anchoring the kinds of large scale semisubmersible vessels or drill ships used for offshore exploration and well servicing, which is done with the aid of separate anchor handling vessels, using massive anchors and may require multiple anchors.